AQP4 and myeloid sarcoma: It should not go unmentioned that other factors than panel composition may influence the frequency of a positive MRZ reaction in a given cohort: (1) It has been shown that the MRZ reaction is virtually absent in important MS mimics such as myelin oligodendrocyte glycoprotein (MOG)-IgG-positive encephalomyelitis (MOG-EM; also termed MOG antibody-related autoimmune disorder, or MOGAD) [13, 15, 16] and aquaporin-4 (AQP4)-IgG-positive neuromyelitis optica spectrum disorder (NMOSD) [10, 14, 17, 32], ADEM[8, 11], paraneoplastic neurological disorders [8, 9] and neuroborreliosis [1, 8].